In recent years, from a social requirement of a lower fuel consumption and a less exhaust emission, an electric vehicle and a hybrid vehicle, each of which is mounted with an AC motor as a power source of a vehicle, is drawing attention. For example, in some of the hybrid vehicles, a DC power source made of a secondary battery or the like and an AC motor are connected to each other via an electric power conversion unit constructed of an inverter and the like, and a DC voltage of the DC power source is converted into an AC voltage by the inverter to thereby drive the AC motor.
In a control device of an AC motor mounted in the hybrid vehicle and the electric vehicle like this, there has been known a technique in which a current sensor for sensing a phase current is not provided in two phases or three phases but is provided only in one phase to thereby reduce the number of the current sensors, thereby reducing the size of a portion near a three phase output terminal of the inverter and reducing the cost of a control system of the AC motor. For example, in a patent document 1 is described a control device of a three-phase AC motor that calculates a current estimated value of a phase (for example, U phase and V phase) other than “a sensor phase” (for example, W phase) on the basis of a current sensed value of the sensor phase of the one phase sensed by one current sensor, a d axis current command value and a q axis current command value, and an electric angle of the AC motor.
Further, as a control mode of an AC motor have been known “a square wave control mode” capable of increasing a voltage utilization factor more than a sine wave PWM control mode or an overmodulated PWM control mode, which is generally employed. The square wave control mode is different from the sine wave PWM control mode or the overmodulated PWM control mode, which feeds back a d axis current and a q axis current, which are calculated on the sensed values of two current sensors, to make the d axis current and the q axis current follow a d axis current command value and a q axis current command value, and calculates an estimated torque from the d axis current and the q axis current, which are calculated on the basis of the sensed values of the two current sensors, and feeds back the estimated torque to a torque command value so as to make the estimated torque follow the torque command value, thereby controlling a phase of a square wave voltage. In a patent document 2 is described a control device of an AC motor which is provided with two current sensors and senses two phase currents in the square wave control mode by the two current sensors.
By the way, an AC motor mounted in a hybrid vehicle and an electric vehicle is used in the wider ranges of the number of revolutions and an output torque as compared with an AC motor in the other technical field, so that it is desired that the AC motor mounted in the hybrid vehicle and the electric vehicle can be applied to a sine wave PWM control mode and an overmodulated PWM control mode, which correspond to “a current feedback control mode”, and a square wave control mode, which corresponds to “a torque feedback control mode”. The square wave control mode is employed in a high rotation operating range, in particular, in which a weak field control for preventing a counter electromotive force is required and minimizes an absolute value of a weak field current of a minus d axis current. Further, the square wave control mode can minimize the number of switchings of an inverter to thereby reduce a switching loss. From these characteristics, in the drive control of a motor generator of the hybrid vehicle and the electric vehicle, it is effective to switch and use various control modes in combination according to the operating state of the number of revolutions and the output torque, that is, according to a voltage required for driving the electric motor in such a way that: the sine wave control mode is used in a low rotation range; the overmodulated control mode is used in a middle rotation range; and the square wave control mode is used in a high rotation range. However, “the torque feedback control mode” described in the patent document 2 does not use a d axis current command value and a q axis current command value, so that the technique described in the patent document 1 applied to “the current feedback control mode” cannot be applied to a control mode described in the patent document 2.
[Patent document 1] JP-A-2004-159391
[Patent document 2] JP-A-2010-124544 (corresponding to US 2010/0123418)